Balanced multichannel amplifier for wide amplitude range



July 21, 1953 J. H. LONG 2,646,469

BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE Original Filed March 6, 1946 6 Sheets-Sheet l FIGJ.

I 2 6) ll INVENTOR JOHN H. LONG ATTORNEY July 21, 1953 J. H. LONG 2,646,469

BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE Original Filed March 6, 1946 6 Sheets-Sheet 2 INVENTOR JOHN H. LONG ATTORNEY July 21, 1953 J. H. LONG 2,646,469

BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE Original Filed March 6, 1946 GSheets-Sheet 5 DISTANCE (d) ee'rwszn OOILS DEFLEGTION 5 FIG.6.

Q o INVENTOR O 2 4 6 8 IO JOHN H. LONG RELATIVE RESPO NS E ATTORNEY July 21, 1953 J H. LONG 2,646,469

BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE Original Filed March 6, 1946 6 Sheets-Sheet 4 men GAIN AMPL.

' so J 2 MED. GAIN 1 AMPL. 25

3| 1 2s 1 Low GAIN AMPL. $32

DEFLECTING FORGE INVENTOR |34 JOHN H. LONG @132 BY W ATTORNEY July 21, 1953 J, LONG BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE Original Filed March 6, 1946 6 Sheets-Sheet 5 CHANNEL I TO CRT CHANNEL 2 I l l I I l J FIGJI.

INVENTOR JOHN H. LONG ATTORNEY July 21, 1953 J. H. LONG 2,646,469

BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE Original Filed March 6, 1946 6 Sheets-Sheet 6 CHANNEL I TO CRT I 1 INVENTOR JOHN H. LONG ATTORNEY Patented July 21, 1 953 BALANCED MULTICHANNEL AMPLIFIER FOR WIDE AMPLITUDE RANGE John H. Long, Flushing, N. Y., assignor to the United States of America as represented by the Secretary of the Navy Original application March 6, 1946, Serial No. 652,909. Divided and this application February 21, 1950,'SerialNo. 145,336

4 Claims. (014179-171) My invention relates to measuring systems and more particularly to accurately and instantaneously indicating and recording the relative displacement between two objects.

The present case is a divisional application of Serial No. 652,909, filed'March 8, 1946, now Patent No. 2,538,158, issued January 16,1951;

mIn determining the effect of shock, vibration, etc., on equipment subject thereto, it is necessary to have a record of the instantaneous relative position of portions of the equipment. From this record, it is not only possible to ascertain the maximum deflections of the various components of the apparatus but also .to determine velocity, acceleration, rate of change ofacceleration, etc. From these data, the effect of the disturbance can be evaluated and design changes made accordingly.

It is possible that the distance between two objects may be determined by the use of a magnetic system comprising an exciting coil mounted on one object and excited with a relatively high frequency electric current .and a pick-up coil mounted on the other object adapted to respond to the magnetic field produced by current flow in the first coil. Inasmuch as the strength of the magnetic field and hence the induced voltage in the pick-up coil is dependent on the distance fromthe exciting coil, the induced voltage is a measure of displacement. As the frequency of excitation may be very high, the induced voltage is a practically instantaneous measure of the distance between the two coils and therefore of the relative position of the two objects subjected tothe shock, vibration, or other disturbance. A record of this voltage therefore provides the desired record of relative displacement.

As a means of measuring displacement, the above-mentioned arrangement has several disadvantages. One of these is the capacitive coupling between the two coils. This coupling, due to capacitance between the turnsof the coils, between the coils and intermediate objects, and between coils and the power supply leads, introduces a disturbing factor in the calibration of the system and prevents obtaining an accurate record of displacement since the capacitance may be due to changes other than relative displacement.

A second disadvantage of the above measuring systems is the inability of these systems to provide an accurate permanent record of the relative displacement between the two objects. This inability arises from the fact that the induced voltage in the pick-up coil generally changes over an extremely wide range even though the motion 2 of the two coils is small. Hence, under a particular condition of motion, these devices require that an estimate be made of the total displacement to be expected and the scale of the recording equipment set so that a record will always remain in the recording film. This method not only requires a preliminary estimate of the total expected deflection but also obtains a complete record only at the expense of inaccuracy in the lower portions of the range. While this difiiculty can be avoided by the use of large record film, the expense and size of thisprocedure is undesir- .able.: i

In accordance with my invention, the above mentioned disadvantages of these magnetic displacement measuring devices are obviated by the use of a balanced exciting and pick-up system, together with a recording system having an automatic scale change.

Use of a balanced excitation system, and pickup coil, together with a, balanced amplifying and recording system, causes the various electrostatic capacitances between the excitation system and the recorder to be neutralized. This prevents the effects of capacitive coupling and renders the entire system independent of changes which alter stray capacitances. In, particular, intermediate objects'betweenthe pick-up and excitation coil, power supply leads, and other sources of stray capacity may move without producing a changed indication on the recording system.

In accordance with a further aspectof this invention, the accuracy of a distance recording system is improved without the use of alarge film size by automatically and instantaneously changing the scale of the recording in accordance with the voltage at the pick-up coil. When this voltage causes-the recording to exceed the available film width with the particular amplification in operation, the amplification is automatically decreased ln definites'teps of known. and predetermined sizeythereby limiting the record tothe available film width and rendering the measurement quantitative for, all ranges of amplification, the amplification being known and fixed in each of the several steps, and the particular step employed being readily determinable by inspection of the record, where, changes of amplification appear as sudden discontinuities in the trace.

Also in accordance with my invention, the instantaneous change in calibration is achieved by firing a gas discharge tube as the signal to be recorded reaches the limits of the recording film. By causing conduction of the gas discharge tube to prevent operation of an amplifier having a 3 high degree of amplification and simultaneously Causing operation of an amplifier having a lower degree of amplification, this change in scale is achieved.

My invention further resides in increasing the eifective recording film Width to any desired degree by combining separate scale changing systems to act successively as the pick-up coil voltage progressively increases.

My invention further resides in features of construction, combination, and arrangement herein described or disclosed whereby an image is presented on a cathode ray tube representative of the displacement between the two objects in a form suitable for visual observation or recording on a permanent film and in a manner giving instantaneous response.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment. It is to be understood, however, that I do not intend to limit the invention by such disclosures for I aim to cover all modifications and alternative constructions falling within the spirit and scope of the invention as defined in the appended claims.

In the drawings:

Figure 1 shows a simple diagram of an elementary system for magnetically determining the distance between two objects.

Figure 2 shows how electrostatic capacitance influences the operation of the system shown in Figure 1.

Figure 3 shows a circuit similar to that of Figure 1 but adapted for balanced operation of the excitation and pick-up coils.

Figure 4 shows the equivalent electrostatic capacitances of the system in Figure 3.

Figure 5 shows an alternate method whereby the operation of a magnetic distance measuring system may be balanced with respect to capacity couplings.

Figure 6 shows the response of a system such as that of Figure 5.

Figure 7 shows a partially schematic and partially isometric view of a recording system adapted for use with a magnetic distance measuring system.

Figure 8 shows in block form how I accomplish an automatic scale change of the recording system.

Figure 9 shows how the response curve of the magnetic distance recording system is divided for an automatic scale change.

Figure 10 shows how displacements appear on the film of Figure 7.

Figure 11 shows a schematic circuit of a twoscale automatic system.

Figure 12 shows a schematic circuit diagram of an automatic system adapted to change the scale range automatically over three difierent scales.

Figure 13 illustrates a simple embodiment of the invention for measurement of instantaneous deflections of a plate.

Referring now to Figure 1, generator I, coil 3, and condenser 2 comprise the exciting system for a magnetic distance measuring device. Coil 3 is caused to resonate at the frequency of generator I, preferably 10,000 cycles by the use of shunt condenser 2. This reduces the magni tude of the current required from generator I to achieve a particular value of magnetic flux within coil 3 and induced voltage in the pick-up coil. The pick-up system comprises coil 4, coridenser 5, tube 6, output transformer 9, resistance 1 and battery 8. Condenser 5 tunes coil 4 to resonance at the frequency of generator I, thereby producing a maximum voltage at the grid of tube 6 for a particular value of distance between coils 3 and 4, Resistance 1 provides grid bias for tube 6 and battery 8 supplies plate supply potential. Output voltage is taken across terminals I0 and I I of output transformer 9.

A voltage appearing at the grid of tube 6 comprises two components, one component due to induced voltage in coil 4 due to magnetic flux from exciting coil 3-. The second component comprises a voltage at the grid of tube 6 due to electrostatic capacitance between the circuit of the excitation system and tube 6, Figure 2 shows the nature of this capacitance. In the figure, condenser I2 represents the weighted value of capacitance between coils 3 and 4 due to the distributed capacitance between the turns of coil 3 and the turns of coil 4 and to intermediate objects having capacitance to both coils. This condenser is in efiect a coupling condenser between the circuit of generator I and the circuit of tube 6 and accordingly produces a component in the output voltage at terminals I0 and II.

Since the capacitance I 2 includes in par-t stray capacitance between the two coils caused by external objects, movement of these objects relative to the coils influences the value of the pickup voltage. Hence the output voltage at terminals I9 and I I, Figure 1, not only indicates the relative position of coils 3 and 4 but also the position of other objects which are not intended to influence the results. It is for this reason that the magnetic distance recording system shown in Figure 1 is unsatisfactory in operation except under conditions wherein the electrostatic capacitance between the exciting and pickup systems is negligible.

Figure 3 shows a balanced system wherein electrostatic capacitance between coils 3 and 4, due to direct capacitance or due to the presence of adjacent objects, is neutralized. In this circuit, the center taps of coils 3 and 4 are grounded instead of one end as shown in Figure 1. In this case, an equivalent circuit showing the electrostatic capacitance between the grid circuit of tube 6 and the exciting circuit is as shown in Figure4. On the grid side of coil 4, two capacitance components exist, the first, I3, is between the grid end of coil 4 and one end of coil 3 whereas the other, I5 is between the grid end of coil 4 and the opposite end of coil 3. Similarly, the cathode end of coil 4 is coupled by capacitances I4 and It to the opposite ends of coil 3. Inasmuch as the voltages appearing at the opposite ends of coil 3 are out of phase and capacitances I3 and I5 and I4 and I6 are nearly identical, the value of induced voltage in the grid circuit of tube 6 due to electrostatic capacitance is negligible and the output voltage at terminals l 0 and I I is not influenced by this capacity.

Figure 5 shows an alternate method wlierel'iy balanced operation of a magnetic distance measuring system may be secured. In the figure, the generator I of Figure 1 is replaced by two generators i? and I3 having a grounded common terminal and producing equal voltages having a 180 phase relation. This may be accomplished by the use of a conventional push-pull oscillator circuit or by a balancing circuit connected to a single ended oscillator. In either case and in the showing of Figure 3, excitation of the exciting ass-6,4 9

"coil 1% is equal and opposite at the two ends thereof, orabout the electricalimpedance center of the coil. Coil i is likewise excited symmetrically about its impedance or electrical center. In addition to this modification, Figure 5 illustrates the use of a push-pull amplifier circuit attached to coil 3. ,In this case the grid circuits of tubes it andiifi are connected to opposite ends of coil :3 and a push-pull output transformer 23 is used. Plate supply voltage for tubes l9 and 20 is supplied from battery 22 and grid bias supplied from resistance 2!. This push-pull circuit has the advantages of being balanced throughout with respect to. ground so that leads to filament circuit, plate voltage supply circuit etc., produce no unbalanced capacities to the exciting system which may influence the results.

.Figure 6 shows a response curve typical of that obtained from a system such as shown in Figure 5. The figure showsthe relative response which may be obtained. in an impedance connected across terminals I6 and H or voltage at these terminals for various values of distance between the two coils. It is evident from the curve that a relatively great change in distance when the coils are separated produces the same change in response as a relatively small change in distance when the coils are close together. Hence to achieve a particular accuracy in measuring the distance between the coils, it is necessary to have an extremely accurate measurement of current at the low value of current as compared with the accuracy of measurement at relatively high values of current. For this reason, conventional recording systems will not provide satisfactory operation with a system such as that of Figure 5.

A recording system adapted for use in connection with a system such as; that of Figure 5 is shown in Figure 7. In the figure, 24 is a cathode ray tube having horizontal deflection plates 25 and 26 connected to output terminals Ill and H. Signals from generating coil 3 are impressed on pick-up coil 4 and appear as an alternating voltage across deflection plates 25 and 26, thereby causing a vertical motion of the cathode ray tube beam in accordance with the magnitude of the induced voltage. Since the beam has no horizontal motion across the screen, the image appears line as shown at 21. By providing film 28 moving at a rapid rate across the image 2'4, a record is obtained of the changes in magnitude of this image.

With a film 28. of reasonable dimensions, it is not'possible to obtain an accurate record of displacement between coils 3 and 4 if any reasonably large change in displacement takes place. The cause of this is evident from examination of Figure 6. Suppose, for instance, the distance between the coils changes from, 8 feet to 2feet at a uniform rate. In this case, the change from Sfeet to 6 feet will cause-a change in output signa1 El of .1 to .4 unit, a change of .3 unit. On the other hand, the change from 4 feet to 2 feet involves a change of 1.2 to units, a otal difierence of 8.8 units, almost 30 times as great. It is, therefore, necessary to 'measure displacement in part of the scale range to an accuracy 30 times as great as the rest of the range.

I have found that the need for a large film 28 may be avoided by an automatic switching system adapted to change the scale of image 2'? I progressively in accordance with the value of the voltage at terminals Ill and II. This system is shown in block form in Figure 8, Attached to terminals i 0 andxl-l are a number .of amplifiers,

such as the three amplifiers 29, 36 and 3f. fhe output of these amplifiers is connected directly to cathode ray tube deflection plates 25 and 26. Amplifier 29, for instance, is adapted to operate with a high degree of amplification so that when low values of input signals appear across terminals l0 and i l, a relatively large deflection of the cathode ray tube beam is obtained if this amplifier is operating. Amplifier 30, for instance, is adapted to produce an intermediate amount of amplification so that the deflection of the cathode ray tube beam is somewhat smaller for the same signals at terminals l0 and H than is the case of amplifier 29. Similarly, amplifier Si is of even lower amplification so that the three amplifiers together provide a large range of suecessive amplification and permit readable signals on the recording film over a very large range in voltage appearing across points I!) and H. In addition to providing amplifiers 29, 39, and 3| with difierent values of amplification, I provide a progressive automatic switching system whereby only amplifier 29 is caused to be operative when signals within its most eifective range are received, and amplifier 3| operates when signals within its most effective range are received. Hence, the system automatically adjusts itself to provide output signals within the scale range of film 28, Figure '7, even though the variation in voltage at terminals Ill and l I is extremely large.

Now referring to Figure 9, the method of establishing the amplifier ranges is shown in detail. Suppose, for instance, the distance between the pick-up coils and the transmitting coils varies from 2.5 feet to 4 feet and it is desired to cause the system to record the variation in voltage output in three progressive stages having equal percentage accuracy. To do this, I set amplifier 29 to operate between output signals D and C, Figure 9; amplifier 3G to operate between output signals C and E, Figure 9; and amplifier 3i to operate between output signals B and A,

Figure 9. These four values of output signal setting are arranged in geometric series relationship so that the same ratio exists between C and D, B and C, and A and B.

Figure 10 shows in detail the appearance on the recording film of various signals correspcnding to the limits of operation of the three amplifiers and with the three amplifiers in operation. From the figure, it is evident that with amplifier 3| in operation (low amplification) signals A and B appear within the range of the recording film, but that signals C and D are too small to appear thereon. On the other hand, with amplifier 3D in operation (intermediate amplification) signals B and C appear on the film but signal D is too small to appear on the film and signal A is too large. If amplifier 29 is operating (maximum amplification) signals C and D appear on the film but signals A and B extend completely across it and do not result in any usable indication.

Figure 11 shows a circuit diagram of a two channel amplifier adapted for automatic switch in in accordance with my invention. In the figure, terminals 32 and 33 comprise input terminals which would ordinarily be connected to terminals such as It) and H, Figure 7. Potentiometer 34 is connected to terminals 32 and 33 and supplies grid voltage to tubes 35 and 36. Cathode bias for these tubes is supplied by resistances 3'! and 38, together with resistance 52. Plate supply voltage for these tubes is supplied through battery 40 and the primary winding of output transformer 39. The second channel comprises tubes 43 and 44 fed from terminals 32 and 33 by potentiometer 42. Cathode resistances 45 and 46, together with resistance 53, provide cathode bias for this channel. Plate supply voltage is derived from battery 48 in the same manner as in the case of tubes 35 and 33. Output signals from both channels are applied to transformer 38 having its secondary connected to the deflection plates of a cathode ray tube.

In order to automatically switch from channel I, Figure 11, to channel 2, the tubes 47 and 48 and the associated circuits are provided. Tube 47 is a gas discharge tube having its cathode circuit connected by resistance 52 to ground and its grid connected by potentiometer 4| to the output voltage of transformer 39. Plate supply voltage for tube 4'! is supplied from battery 54 and resistance 49. Tube 48 is a vacuum tube having its grid connected by the resistances 58 and into the plate circuit of tube 4? and its cathode connected by resistance 53 to ground. Plate supply voltage for tube 48 is supplied directly from battery 54. The cathode of tube 4': is connected to the cathodes of tubes and 33 by resistances 38 and 3'! whereas the cathode of tube 48 is connected by resistances and 46 to the cathodes of tubes 43 and 44.

Operation of the circuit of Figure 11 is as follows. When output voltage across transformer 39 is below a predetermined level established by the characteristics of tube 47, the setting of potentiometer 4|, and the value of voltage of battery 54, tube 4'! never reaches the firing point. Hence, no plate current passes through the tube 4'! and the grid of tube 43 is at a high positive potential determined by battery 54 and resistors 48, 58 and 5|. Hence, tube 48 draws a high space current, resulting in a large value of voltage drop across resistance 53 which in turn biases tubes 43 and 44 beyond the cut-off point and prevents operation of channel 2. Inasmuch as no space current passes through tube 4?, the voltage drop across resistance 52 is only that due to operation of tubes 35 and 36 and amplifier channel operates in the normal manner. Hence, so long as the output voltage or transformer 39 is below the predetermined level, only channel I is operative and the deflection of the cathode ray tube beam corresponds to the amplification in this channel.

When the output voltage appearing across transformer 39 exceeds the value required to fire gas discharge tube 47, space current fiows therethrough. This current causes a voltage drop across resistance 52, thereby biasing tubes 35 and 33 beyond the cut-off point and preventing operation of the amplifier channel I associated with these tubes. In addition, the space current flow through tube 4'! causes a voltage drop in resistance 49 which reduces the grid voltage at tube 48 thereby reducing space current flow therethrough to the point at which negligible voltage drop is produced in resistance 53. Hence, amplifier channel 2 is operative and a deflection at the cathode ray tube corresponding to the amplification of this channel is obtained. By properly setting the values of potentiometer 34 and 42, together with potentiometer 4| and the characteristics or" the circuit of tube 41, the range of the two channels is established to divide the the range of the output voltages in a manner providing maximum optimum performance. Inasmuch as the circuit is instantaneous in operation, the change is completely automatic and I obtain a useful record over the entire range of input signals.

Figure 12 shows a schematic circuit diagram of a system utilizing three amplifier channels having automatic switching circuits which provide progressive operation in accordance with increasing signal level. In the figure, input signals are supplied to terminals 55 and 56 which in turn are connected to potentiometers 51, 62 and 15 leading to the three separate amplifier channels. Tubes 58 and 59 comprise the first amplifier channel. The control grids of these tubes are connected to potentiometer 51 and the cathodes to bias resistances 68, 6| and 18. Tubes 63 and 64 comprise the second amplifier channel, being connected to potentiometer 62 and cathode resistances 65, 66 and 84. Tubes 1| and 12 comprise the third amplifier channel. The control grids of these tubes are connected to potentiometer 15 and the cathodes to resistances 13, 14 and 88. Output transformer 68, together with plate supply source 61, is connected to all three amplifier channels. The secondary of output transformer 68 leads to the cathode ray tube deflecting circuit and to potentiometers 69 and 10. The automatic selection system comprises tubes 16, 8|, 82 and 81 and their associated circuits. Tubes 16 and 82 are gas discharge tubes having their grids connected to potentiometers 68 and 10. The plate of tube 16 is connected through resistance H and switch 90 to plate supply voltage source 89. The grid of tube 8| is connected by resistances 18 and to the plate of tube 76. The plate of tube 8| is connected directly to the plate supply voltage source 89. The cathodes of tubes 8| and 82 are connected to common cathode bias resistance 84. The anode of tube 82 is connected by resistance 83 and switch 9| to plate supply voltage 88. The grid of tube 81 is connected by resistances 85 and 86 to the plate circuit of tube 82.

Operation of the system shown in Figure 12 is as follows. With switches 80 and 8| closed and gas discharge tubes 16 and 82 in the non-conducting condition, input signals at terminals 55 and 56 below a predetermined level will not cause a suificient voltage to appear at tube I6 to cause it to conduct. Hence, no space current due to tube 16 passes through resistance 18 and the operation of the channel comprising tubes 58 and 58 is normal. Inasmuch as the grid of tube 8| is provided with a high positive potential by reason of the circuit comprising resistances 11, I8 and 80, a large space current flows through this tube, thereby causing a high voltage drop in resistance 84 which cuts off plate current flow in tubes 63 and 64 and prevents operation of the amplifier channel No. 2. Similarly, tube 8'! draws a high value of plate current, thereby preventing operation of tubes TI and 12 and channel N0. 3. When the output voltage of transformer 68 reaches a predetermined value, tube 16 fires, thereby causing plate current fiow through resistance l8 and biasing tubes 58 and 59 beyond the cut-off point. Operation of channel No. 1 is thereby prevented. The voltage drop in resistance 17 reduces the grid voltage at tube 8| below the cut-off point, thereby reducing the voltage drop in resistance 84 to the point at which amplifier channel No. 2 (tubes 63 and 64) is operative. If the voltage appearing at terminals 55 and 56 further increases to the point at which output voltage from transformer 68 is sufiicient to fire tube 82, plate current flow takes place through this tube, thereby causing voltage drop in resistance 84 suificient to bias tubes 63 and 64 to the cut-off point and preventing operation of channel No. 2 of the amplifier. However, the

voltage drop in resistance 83 is sufficient to cause decreased plate current flow in tube 81 and reduce the bias of tubes H and I2 below the cutoff point. Operation of channel No. 3 is then possible. Hence, the three amplifiers are automatically switched to change the scale range of the cathode ray tube in accordance with the variation in input voltage at terminals 55 and 56, the, changes taking place when the input signals reach predetermined levels.

Adjustment of the amplifiers in Figure 12 is obtained by changing the resistance values at potentiometers 51, 62 and I5. These are adjusted until the overall amplification of the three am-v plifiers is such as to provide overall amplification values as shown in Figure 10. The transition from one amplifier to the next is controlled by the setting of potentiometers 69 and ID, together with the characteristics of tubes 82 and I6 and the value of voltage source 89, the settings of said potentiometers being such that gas discharge tube It is fired at a slightly lower output potentia1 than the output potential at which gas discharge tube 82 is fired. These values I adjust so that the transition occurs at voltage values 38 and C, Figure 9. Hence, as the output voltage changes from point D, Figure 9 through points C and B to A, Figure 9, the three amplifier channels are successively operated. When the various amplifiers are brought into operation, a sudden change in the trace on the recording film will be shown which can be used to indicate the change. Hence, a large range in output signals is recorded on a film of small area. Switches 90 and SI serve as manual reset means.

The amplifiers are switched on successively according to either an increasing or decreasing level of amplification. The circuits may be designed to measure objects moving toward each other or away from each other. The circuits shown, however, are not automatically reversible and the same circuit may not be used for both movements without modification.

A simple embodiment of the invention is illustrated in Figure 13, wherein the plate I30 is mounted in blocks as at I32 and has thereon the pillars I 33 and H54 on which is secured the one or more turns of the coil H3, energized from oscillatory source III, such as the generators IT and I8 of Fig. or other oscillation source. The pick-up coil I M is shown similarly mounted on a fixed base I36 by supporting structure I35, and electrically connected to the receiver circuit. Any initial separation of the coils H3 and H4 may be designated, and a displaced position of the plate I30 is shown at lat with a corresponding displaced position of coil H3 at H3, the separation thereof from coil I M being illustrated at d. The diiierence between the distances (2 and d is a deflection, and since the device illustrated in Figures 3 and 5 provides an instantaneous measure of this distance at all times, it measures deflections as a very fast acting deflection gauge.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. The combination comprising first, second and third amplifier channels having diilierent respective gains; a common input and a common output circuit for said amplifier channels; a con- 10 trol circuit for said amplifier channels comprising: a first, second, third and fourth discharge device each including control, anode and cathode electrodes; a source of direct current energizing voltage for said: discharge devices; a first impedance between the anode of said first discharge device and the positive terminal of said source of direct current energizing voltage, and a second impedance between the cathode of said first discharge device and the negative terminal of said energizing voltage source; means coupling the control electrode of said first electron tube discharge device to the said common output circuit of said amplifier channels for rendering said first discharge device conductive when the amplitude of the signal in said common output circuit exceeds a first amplitude level, means coupling the voltage developed across said second impedance to said first amplifier channel to render said first amplifier channel inoperative only upon conduction of said first electron tube discharge device; direct current coupling means for coupling the voltage at the anode electrode of first discharge device to the control electrode of said second discharge device to render the latter said device conductive only' when said first discharge device is non-conductive; a third impedance coupled between the cathode electrode of both said second and third electron discharge devices and the negative terminal of said source of energizing voltage; means coupling the anode electrode of said second discharge device to the positive terminal of said source of energizing voltage; a fourth impedance coupled between the anode electrode of said third discharge device and the positive terminal of said source of energizing voltage; means coupling the voltage developed across said third impedance to said second amplifier channel to render same inoperative upon conduction of either said second or third discharge devices; means coupling the control grid of said third discharge device to the said common output of said amplifier channels for rendering said third discharge device conductive when the amplitude of the signal in said common output exceeds a second amplitude level which is higher than said first amplitude level; direct current coupling means for coupling the voltage at the anode electrode of said third discharge device to the control electrode of said fourth discharge device to render the latter said device conductive only when the said third discharge device is nonconductive; a fifth impedance connected in series circuit relation between said cathode of said fourth discharge device and the negative terminal of the source of energizing voltage; and means coupling the voltage developed across said fifth impedance to the said third amplifier channel for rendering same inoperative upon conduction of said fourth discharge device.

2. The combination comprising a first, second and third transmission channels; a first source of control voltage of varying amplitude; control means for rendering said transmissions channels operative in accordance with the amplitude of the voltage from said first control voltage source comprising: a first, second, third and fourth discharge device each including control, anode and cathode electrodes; a source of direct current energizing voltage for said discharge devices; a first impedance between the anode of said first discharge device and the positive terminal of said source of direct current energizing voltage, and a second impedance between the cathode of 'i-l -said first discharge device and the negative terminal of said energizing voltage source; means coupling the control electrodes of said first electron tube discharge device to the said first control voltage source for rendering said first discharge device conductive when the amplitude of said control voltage exceeds a first amplitude level; means coupling the voltage developed across said second impedance to said first transmission channel to render said first transmission channel inoperative only upon conduction of said first electron tube discharge device; direct current coupling means for coupling the voltage at the anode electrode of said first discharge device to the control electrode of said second discharge device to render the latter said device conductive only when said first discharge device is :nonconductive; a third impedance coupled between the cathode electrode of both said second and third electron discharge devices and the negative terminal of said source of energizing voltage;

,ffier channel to render same inoperative upon conductionof either said second or third discharge, devices; means coupling the control grid I tudelevel which is higher than said first amplitude level; direct current coupling means for coupling the voltage at the anode electrode of saidisource of energizing voltage; means coupling the voltage developed across said fifth impedance to the said third transmission channel for rendering s'ameinoperative upon conduction of said fourth discharge device.

3. The combination comprising a first amplifier :channel having a 'fixedrfinite predetermined gain, a second "amplifier channel having a fixed gain substantially greater than that of said first amplifier-channel, first coupling means for coupling a given signal to be amplified simultaneously to the inputs of both of said amplifier channels, second coupling means coupling the output circuits of said amplifier channels to a common output circuit, control means including a gaseous tube discharge device ofatype wherein the control grid loses control immediately after the firing thereto and including anode and cathode electrodes, a vacuum tube discharge device including control, cathode and anode electrodes, a source of energizing voltage for said discharge devices, respective impedances in series with said gaseous and vacuum tube discharge devices and oi said thir'd discharge device to the said first a j icorrti ol voltage source 'for rendering said third .dis charge device conductive when the amplitude "of said control voltage exceeds a second ampli-= said source of energizing voltages, third coupling means including a coupling circuit extending between the control grid of said gaseous tube discharge device and the said common output of said amplifier channels for causing the firing of said gaseous tube discharge device when the amplitude of the signal in said common output exceeds said predetermined range of amplitude values, fourth coupling means coupling the voltage developed across the said impedance in series with said gaseous tube discharge device to one of said amplifier channels to render one of the channels thereof inoperative, means rendering said vacuum tube discharge device conductive duringtnon-conduction of said gaseous tube discharge'device and non-conductive during conduction of; said gaseous tube discharge device, and fifth coupling means coupling the voltage across said impedance in series with said vacuum tube discharge device to the other one of said amplifier channels to render same inoperative upon conduction of said vacuum tube discharge device. H 4; lhe combination comprising a first amplifier channel having a fixed finite predetermined gain, a second amplifier channel having a fixed gain substantially greater than that of said first anip lifie'r channel, first coupling means for coupling a given-signal to be amplified simultaneously to the inputs of both of said amplifier channels, second coupling means coupling the output circuits of said amplifier channels to a common outputfcircuit, control means including first and second-electron discharge devices each including thode and control electrodes, a source df'energiz'ing voltage for said discharge devices, respective i'mpedances in series with said first and s econd; electron tube discharge devices and said source of energizing voltage to form respective electronic switch circuits, third coupling ineansiioupling said'two electronic switch circuits together. so that conduction ofone electron tube discharge-device results in non-conduction of the other electron tube discharge device, fourth couplingme'ans coupling the said common output of said amplifier channels to the control grid of one-ofs'aid electron'disch'arge' devices for rendering-same conductive when the signal in the output of said amplifier exceeds said predetermined range of r values, and fifth and sixth coupling means coupling the respective voltages developed Number 1 Name Date 1 1,711,658 Spra'gue May 7, 1929 2,253,832 Whitaker Aug. 26, 1941 2,324,314 Michel July 13', 1943 2,396,395 Smith et al Mar. 12, 1946 2,457,214 D011 et a1 Dec. 28, 1948 2,464,353 Smith et a1 Mar. 15, 1949 2,482,759 Goodrich et a1. SeptVZ'Z, 1949 

